The present invention relates to a turbo-charging apparatus for a vehicle engine, and particularly relates to a turbo-charging apparatus for a vehicle engine that is equipped with a first turbocharger and a second turbocharger arranged in series with the first turbocharger.
Conventionally, diesel engines are known in which a fuel consumption can be improved by reducing a mechanical resistance of, for example, bearings through a decrease of a compression ratio in a compression stroke and NOx contained in exhaust gas can be reduced by decreasing a combustion temperature through the decrease of the compression ratio. However, an engine output is reduced when the compression ratio is decreased as described above. For this reason, as an effective method of suppressing the reduction of the engine output while decreasing the compression ratio, a turbo-charging apparatus for turbo-charging intake air by using kinetic energy of the exhaust gas discharged from the engine is widely adopted.
In such turbo-charging apparatuses, there exists a sequential turbo-charging apparatus including a compact turbocharger for turbo-charging the intake air mainly under a low speed and low load situation and a large turbocharger for turbo-charging the intake air mainly under a high speed and high load situation, and the sequential turbo-charging apparatus can switch turbo-charging characteristics of the compact turbocharger according to an operation state of the engine.
JP2003-239752A discloses a turbo-charging apparatus including, on one side of an engine, a first turbocharger with a larger capacity and a second turbocharger with a smaller capacity arranged at a position higher than the first turbocharger. A second turbocharger compressor is arranged downstream from a first turbocharger compressor, and an intercooler is arranged upstream from a coolant cooler and between the first turbocharger compressor and the second turbocharger compressor. Thereby, an intake pipe between the intercooler and the second turbocharger compressor is minimized in its length and an arrangement space is saved.
The diesel engine includes a large exhaust filter device, for example a DPF (diesel particulate filter), for purifying the exhaust gas, therefore, an arranging layout containing the exhaust filter device in addition to the compact turbocharger and the large turbocharger is proposed.
JP2006-070878A discloses a turbo-charging apparatus including, on one side wall of an engine, a compact turbocharger, a large turbocharger, and a DPF connected with a turbine outlet of the large turbocharger. The large turbocharger is arranged below the compact turbocharger to be offset therefrom, the DPF is arranged below the compact turbocharger and at substantially the same height as the large turbocharger, and an exhaust gas introducing port of the DPF is arranged with its opening facing toward the large turbocharger turbine. Thereby, the DPF, the compact turbocharger, and the large turbocharger can be arranged compactly on the side wall of the engine, the exhaust gas with small exhaust energy loss and high temperature can be obtained, and a turbo-charging performance and a regeneration efficiency of the DPF are improved.
In the turbo-charging apparatus disclosed in JP2003-239752A, the intake pipe can be shortened by arranging the large first turbocharger and the small second turbocharger in two vertical levels. Because the large sized component such as the DPF is equipped near the engine, a layout efficiency is required for, for example, an exhaust pipe and the components in the exhaust system other than the intake pipe. However, no description of a specific layout for the exhaust filter device, such as the DPF, and the components in the exhaust system, such as the exhaust pipe, exists in JP2003-239752A.
In the turbo-charging apparatus in JP2006-70878A, an arrangement space is formed rearward of the engine, and a turbo-charging gas pipe can be installed by utilizing the arrangement space. However, because an inter-turbine passage connecting a discharging part of the compact turbocharger turbine with an introducing part of the large turbocharger turbine passes around the compact turbocharger turbine and is positioned above the compact turbocharger turbine, the inter-turbine passage is formed in a substantially U-shape and the passage length may be long. Thus, a thermal energy of the exhaust gas is discharged outside and such problems as, for example, a decreased turbo-charging efficiency, a decreased regeneration efficiency of the DPF, and a delayed activation of a catalyst become concerns due to a decreased kinetic energy of the exhaust gas when the passage length between the turbines is long.